Various types of local area communication networks are known, and such a network is used for example to communicate computer, video, packetized voice, and facsimile data within a single business office. One such network is described in the article by J. O. Limb and C. Flores, entitled "Description of FASNET-A Unidirectional Local Area Communications Network", Bell System Technical Journal, vol. 61, no. 7, September, 1982. The FASNET is an implicit token-passing, local area network aimed at supporting high data rates and carrying a wide mix of traffic such as data, voice, video and facsimile. The transmission is unidirectional with stations passively attached to the medium via unidirectional couplers. The unidirectional transmission provides efficient operation at high data rates with high reliability.
Although the FASNET network is an extremely efficient network, there exists a problem in the interconnection of multiple FASNET networks because of the use of only address information to control the internetwork transmission of packets. Such a proposal for interconnecting FASNET networks is detailed in the previously mentioned article. In this article, the interconnection proposal uses gateway stations which provide interconnection paths between the networks. A packet, which is to be transferred from a first FASNET network to a second FASNET network, is initially transmitted to the gateway station on the first FASNET network. For this transmission to occur, it is necessary for the address of the gateway station to be included in the packet and then for the packet to be transmitted from the gateway station of the first FASNET network to a second gateway station within the second FASNET network. The latter then inserts the proper address information so that the packet can be transferred to a station on the second or another FASNET network. A deficiency in such an arrangement is that the second gateway station must have access to all addresses of destination stations which it serves and must check each packet transmitted on the network to verify whether or not that packet should be transferred to another network. Verification on a per packet basis requires that many accesses be made to the address information and those accesses consume a large amount of real time and accordingly reduce the system's service capacity. Although the Limb et al. system is suitable in many applications, among its recognized deficiencies is that it requires a large number of memory units and associated controllers and does not function well when a large number of stations are being added and subtracted from the various FASNET networks, because the practical difficulties associated with administering and updating address information records which are stored in the memory units become extremely time consuming and complex. No provision is made in the Limb et al. for automatic hunting of functional service units or common resources which are grouped in a common pool to serve originating stations. Such common resources may for example comprise a hunt group of trunk circuits connected between the FASNET network and a telephone office.
Another example of a local area communication system which utilizes gateway stations for interconnecting networks is disclosed in U.S. Pat. No. 3,749,845; entitled "Digital Data Communication System". That patent discloses the use of central switching units, each attached to a particular network to perform the gateway functions for each network. A switching unit stores internally all address information for identification of stations on the attached network and performs all packet switching functions; and upon detection of a packet address not designating a station attached to the network, the switching unit transfers this packet to another network. A problem in that system is that its performance is limited to the throughput of the switching unit, because it must perform a multitude of packet processing and switching operations.